Are DUI Breath Test Results Always Accurate?

By |2022-06-14T11:59:50-04:00June 14th, 2022|Categories: DUI Driving Under the Influence|Tags: , , , |

Breathalyzer accuracy is a major talking point in DUI cases. After an arrest, many people ask us, “are breath test results accurate?”

In Florida, the law states that a person is guilty of DUI if the driver has a blood alcohol content (BAC) of 0.08% or more at the time they operated a vehicle. However, as criminal defense attorneys, we regularly challenge or explain BAC results of 0.08% and above.

Related: Read our guide on what to do if you’ve been stopped for a DUI in Florida.

Breathalyzer Accuracy

Modern breathalyzers are considered reasonably accurate, but can be error-prone. They’re not perfect and can lead to false results when used incorrectly or with interfering factors.

Judges in some states threw out over 30,000 tests in one year alone – due to human errors and lax oversight.

Thousands of further convictions are at risk, with defendants being acquitted for cases that prosecutors believed they would have won had they been able to show the breathalyzer was inaccurate.

Margins for Error

All breathalyzers have a margin of error, in some cases as much as 0.01%. That might not sound a lot, but it is critical if you consider that it could be the difference between a conviction and no conviction!

Any driver who is slightly above the limit (such as 0.08-0.09%) may have grounds for arguing the margin of error if there is no other evidence to support the belief you were drunk – such as failing a walk and turn test.

Breathalyzers also work by measuring the alcohol concentration in a person’s breath. If that breath contains other substances, then it may trigger an incorrect result. That’s why police officers should observe the driver for around 10-15 minutes before administering a breath test. If that didn’t happen, questions can be raised.

Additionally, the prosecution must prove that your BAC was above 0.08% at the time of driving. When someone consumes alcohol, their body first absorbs the alcohol over time before eliminating it. Everyone absorbs and eliminates alcohol at different rates. Often, law enforcement can wait over an hour before administering the breathalyzer. This gap in time means that the prosecution may have difficulty determining what the BAC was at the time a person was actually driving.

Factors That Can Affect Breathalyzer Accuracy

Foreign Substances

Substances present in the mouth at the time of the test may cause false positives – such as mouthwashes, breath fresheners and alcohol-containing medicines.


Breathalyzers must be calibrated regularly and have fresh batteries to maintain accuracy. If this doesn’t happen, then the results can drift.


Just like computers, modern breathalyzers rely on software. And just like computers, bugs and glitches can occur.

Human Error

Breathalyzers are relatively easy to use but can bring incorrect results if attention to detail isn’t given.


Breath tests should ideally be performed multiple times to prove a consistent and reliable result. This is especially true for fuel cell sensor technology models that perform best with repeated tests.

Environmental Factors

Breathalyzer accuracy may also drift if performed in the presence of fumes, chemicals, varnish and glasses.

What Should I Do If I Think My DUI Breath Test Results Are Incorrect?

If you believe your breathalyzer test results are incorrect, then you should contact a DUI defense attorney immediately.

In some cases, your attorney may be able to determine that your breathalyzer was not calibrated correctly.

Or, they will build a strong defense that proves your results do not show beyond reasonable doubt that you were driving while impaired.

For example, if you performed a walk and turn or other field sobriety test flawlessly, it may show that a small margin could have been an error.

Can I Refuse a DUI Breathalyzer Test?

If you’ve had nothing to drink, you should always take the test as you will likely blow .000. But you should expect to next provide a urine sample.

If you know you’re drunk or are likely over the 0.08% limit or are in doubt, then it can be better to refuse the breath test. However, there are consequences.

In Florida, refusing to blow will result in an immediate driver’s license suspension. You will be unable to drive for at least one year. Additionally, if you have previously refused to provide a breath sample it can result in the criminal charge of refusal as well as a longer driver’s license suspension. However, this still may be an option than facing a conviction for a DUI charge, if the lack of evidence can be used in your favor.

Additionally, if you refuse to provide a sample, you are automatically escalated to “Tier 2” in the State Attorney’s Office’s D.R.O.P. Program. This means there will be enhanced penalties even if you are eligible for the program.

How Do Breathalyzers Work?

Breathalyzers work by measuring how much alcohol is in your breath and providing an estimate of your blood alcohol concentration from that.

This works because alcohol circulates throughout your blood before reaching your lungs – similar to how carbon dioxide leaves the body. Therefore, when you’ve been drinking, you exhale the alcohol.

Breathalyzers work with a breath-to-blood alcohol ratio:

  • For every 1-milliliter of alcohol in your breath, there are 2,1000 milliliters in your blood.

Why Don’t Police Use Blood Tests?

Blood alcohol tests are considered more accurate, so why don’t police officers use them?

The answer is because they’re difficult to perform. Asking someone to provide blood on the side of the road is far from easy, let alone perform it.

But breath tests are simple. They don’t require extensive training or medical licenses. They produce immediate results. In contrast, blood tests require lab results. That being said, Blood tests are still utilized in situations where breath tests are impossible or impracticable.

Florida BAC Results

.05 or Less

If someone provides a breath sample of less than 0.05% BAC, it is presumed they are not DUI. However, that presumption may be overcome by other evidence. Additionally, if you are under the influence of other controlled substances you can be found guilty if the alcohol and other substances combine to the extent that your normal faculties are impaired.

.05 – 0.07

These levels do not give rise to any presumption either that someone is, or is not, impaired.. However, other evidence may be used against you to prove a DUI offense, such as driving behavior, field sobriety test results, and urine samples.

.08 or More

If you blow these results, you are presumed to be guilty of DUI. However, there are still defenses to your case and you should immediately call a Florida criminal defense lawyer.

Contact a DUI Defense Attorney in Florida

If you’ve been arrested for a DUI in Florida, then our DUI defense lawyers can help. Our Florida criminal defense attorneys can fight on your behalf to help you avoid jail time and avoid a criminal record.

There are many different routes to defense, from proving the arrest or traffic stop was unlawful to showing your breathalyzer test results were inaccurate.

Free Consultations

Ranger Jackson is a top-rated criminal defense attorney in Pinellas County. He is an associate at Battaglia, Ross, Dicus & McQuaid, P.A., one of Tampa Bay’s most prestigious law firms with the reputation and connections to make things happen.

Contact us today for a free consultation to get started or CALL (727) 381-2300